Frac-sand delivery system

ABSTRACT

A frac-sand well site delivery system is a process and method of storing, measuring, metering and regulating the percent solids or PPA (pounds of proppant added) in a sand slurry form. The sand delivery system is a closed loop, on-site storage system that can receive and store frac-sand. The sand delivery system takes the sand directly from the wash plant or a storage site and transports it to a sand storage pit preferably via pipe but trucking can be used when slurry transfer may not be possible. From the sand storage pit, the sand is pumped directly to regulator for mixing into a sand slurry for subsequent delivery to the frac pumps. Optionally a regular frac blender can be used with the regulator and the storage system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent application Ser. No. 16/920,092, filed Jul. 2, 2020, entitled “Wet Frac-Sand Delivery System”, that claims priority from U.S. Provisional Patent Application No. 62/857,147, filed Jun. 4, 2019, entitled “Wet Frac-Sand Delivery System” and U.S. Provisional Patent Application No. 62/947,685, filed Dec. 13, 2019, entitled “Closed Loop Wet Sand Delivery System”, the disclosures all of which are incorporated by reference herein.

FIELD

The present disclosure relates to a frac-sand well site delivery system.

BACKGROUND

The cost of completing a frac-sand well are substantial. Frac-sand, water and pumping equipment are the three primary cost drivers in well completion. The system described herein is focused on the delivery and the metering of frac-sand, wet or dry, at a well site that reduces the cost of completion related to fracturing the well.

Frac-sand was once a highly technical classification for sand that had to meet certain material properties. Roundness and hardness were the two most critical specifications. Operators and service companies have become aware that quality is much less important than quantity when maximizing oil well production. This change in thinking is the principal reason for the boom in local and regional frac-sand production. Moreover, this change has been devastating to the sand industry in the northern states but has dramatically reduced the cost of frac-sand delivered to the well. Oil field basins, where sand deposits are present, have quickly become the most economical basins in the United States. Local and regional frac-sand adoption has reduced the cost of sand effectively by 50 percent when compared to railing northern sand to southern basins.

Many operators have unbundled the well completion process and assumed the cost of delivering sand to the well. The conventional process of producing frac-sand typically requires: (1) harvesting a deposit of suitable sand, (2) washing, drying, screening to size, (3) storage and loading trucks at plant, (4) transporting, (5) unloading and storage at well site. Each process, in itself, is fairly straightforward. However, each transition point from harvesting to blender adds cost to the sand and thus the completion.

An operator incurs significant expense for sand that is sized to two grades, 40/70 and 70/140 (100 mesh). For an operator to produce these two grades, the sand is first washed, and, in this process, the large and small grains in the deposit are cut so that the largest is 40 and the smallest is 140. This is done in the washing process so that the resulting sand grains coming from the wash process is 40/140. This column of sand is fed into a dryer and then to a screening tower and finally to dry storage. From dry storage the sand is loaded into a specialized trailer or other customized box delivery system and transported by truck, often times over large distances, to the well site.

The fracturing process, also known as “fracking” or simply “frac,” involves: (1) the hauling of frac-sand to the well site by means of specialized hauling equipment that can include pneumatic bulk trucks, storage box containers transported on flat bed trucks, or belly dump trucks; (2) the frac-sand is then pneumatically unloaded, augured, or conveyed into temporary storage silos or staked on top of wooden decks, in the case of box containers, by means of fork-lift or special cranes; (3) the frac-sand is then delivered from the temporary storage directly to the frac blender, most commonly via a gravity delivery system or a conveyor belt system; (4) the frac-sand is then metered in a controlled manner to the frac fluid consisting commonly of fresh water or recycled produced water and the necessary frac chemicals to create a sand slurry; (5) the sand slurry is then fed into a manifold known as a frac missile; (6) the frac missile distributes the sand slurry to the high pressure frac pumps; (7) the high pressure frac pumps pump the sand slurry at a high pressure into the well; thus (8) creating fractures in the hydrocarbon barring formation. These fractures are propped open by the frac-sand (also known as proppant) and the fractures serve as pathways for the hydrocarbons to flow into the well. Because the sand slurry is generally required to be mixed at precise concentrations measured in pounds per gallon (lbs./gal) or in Pounds of Proppant Added (PPA), this process involves the use of specialized sand metering equipment equipped with computers, flow, pressure and sand concentration measurements, and control systems that allow the operator to achieve the desired sand concentrations and dynamically make adjustments based on the pump rate throughout the duration of the fracturing treatments that could last dozens of minutes to several hours.

In prior arts, the process of metering the sand is achieved in the frac blender equipped with (1) an auger system that moves the sand from a hopper to a mixing tub controlling the sand concentration by how fast the augers rotate, or (2) with a controlled gate system that controls the sand concentration by how wide the gate opens to allow the sand to gravity fall into the mixing tub.

In the recent years, some operators in the industry started using wet sand in their frac operations instead of dry sand. Wet sand is defined as sand that has moisture content higher than 3% and preferably less than 10%, while dry sand is defined as having 0% moisture content or less than 1%. US 2018/0339278 discusses how wet sand tends to clump up, making it difficult to use with existing sand delivery equipment. US 2018/0339278 proposes a solution to rely on vibratory systems to help liquify the wet sand rendering it easier to auger out of the storage to the tub in the frac blender. In other prior art, the wet sand is hauled to the well site in modified box containers similar to the ones used to transport and deliver sand to the frac blender. Because of the stickiness of the wet sand, however, the boxes are placed on top of vibrating frames that assist the wet sand to fall into a conveyor belt system that is equipped with weight sensors to help meter the sand concentration needed directly into the frac blender mixing tub—bypassing the auger system in the frac blender. Unlike dry sand, auger systems cannot properly handle the metering of wet sand. The reliance on vibrations to help sand delivery does come with a challenge of increased equipment failures and increased maintenance costs due to the added stress on the equipment that is subject to the vibrations. Another challenge with current delivery systems used with wet sand is the difficulty to manage the delivery when operating under freezing temperatures, which may render the wet sand frozen and immovable from the storage containers.

The use of wet sand in the frac process helps operators reduce completion costs and comes with several other benefits such as reduced green-house gas emissions due to eliminating the need to dry the sand. However, a need in the industry exists for a sand delivery system that simplifies the logistics—including the delivery and metering of frac-sand, wet or dry, (a) from the source, (b) through the temporary storage on the well-site, (c) all the way to the high pressure frac pumps, and (d) ultimately into the wells via injection.

SUMMARY

The frac-sand delivery system that is disclosed herein is a process and method of storing, measuring, regulating and metering the concentration of solids, or PPA (pounds of proppant added), in a sand slurry form. The sand delivery system consists of an on-site storage system that can receive and store wet or dry frac-sand with water directly piped and pumped in the form of a concentrated slurry from the sand wash plant, a nearby sand mine, or a centralized sand storage site. The on-site storage can also receive wet or dry sand by any other sand transportation means and then be unloaded into the on-site storage by means of a conveyor system, augers, front loaders, pneumatic suction, or any prior art designed to move aggregates or sand. The on-site storage can be any portable storage tank or an earthen pit. The delivery system delivers and meters the sand concentration needed through a regulator system that enables the circulation of a concentrated slurry in a closed loop back to the storage system, and meters the amount of sand needed into the carrying frac fluid through set regulating valves that open or close at varying degrees to achieve the desired concentration of sand in the frac fluid based on the pump rate and the density of the concentrated slurry originating from the storage system. The controlled opening of the regulating valves allows the concentrated slurry to be combined with the clean stream of the carrying fluid and deliver the mixture at the desired sand concentration to the high pressure frac pumps to be injected into the well. The sand concentration can also be regulated by controlling the rate of injection of the concentrated slurry into the clean fluid stream; in this case looping back the slurry from the regulator to the storage system is not necessary and becomes optional.

The delivery system can also be used to meter the sand slurry to a regular frac blender, eliminating the need for auguring or using a metering conveyor belt. The sand regulator can receive sand slurry from the storage system using, but not limited to, a dredge pump, a centrifugal pump, a vortex pump or an eductor system The sand delivery system may be connected to feed a single well or multiple well sites, well bores, boreholes, or similar fracturing locations.

When pumping sand in a slurry form from the source to the well-site, the sand delivery system eliminates several high cost steps in the fracturing process, such as drying, dry screening, all dry sand storage, and associated equipment on the pad site, including, dry sand silos, wooden deck storage areas, boxes, pneumatic trailers, sand kings, T-belts, sand conveyors, sand augers, and fork lifts. Accordingly, the total cost savings in the completion process is substantially reduced, and the reduction of required equipment personnel for operations likewise provides significant savings. Additional benefits of the sand delivery system include reduced emissions and reduced silica dust on location.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, reference is now made to the following description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.

FIG. 1 is a diagram of a frac-sand delivery system according to one embodiment.

FIG. 2 is a plan view of a well site including a frac-sand delivery system according to the embodiment in FIG. 1.

FIGS. 3A and 3B are a plan view and cross-section view of a sand pit according to one embodiment.

FIGS. 4A and 4B are a plan view and an isometric view of a sand regulator according to one embodiment.

FIG. 5 is a plan view of a well site including a frac-sand delivery system according to another the embodiment.

FIGS. 6A and 6B are a plan view and a side view of a sand regulator according to another embodiment.

FIGS. 7A and 7B are an isometric view and cross-section view of a sand pit according to one embodiment.

DETAILED DESCRIPTION

It should be understood at the outset that although illustrative implementations of one or more embodiments are illustrated below, the disclosed systems and methods may be implemented using any number of techniques, whether currently known or not yet in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, but may be modified within the scope of the appended claims along with their full scope of equivalents.

The frac-sand delivery system may utilize dry sand or wet sand that has been washed and sized but not dried in a dryer. “Wet Sand” is defined as sand with greater than 3% moisture content. Preferably, the wet sand is between 5% to 8%. The wet sand may be a of any mesh size commonly used in the fracturing process such as but not limited to 100 mesh or 40/70 mesh. The frac-sand delivery system may also utilize dry sand. “Dry Sand” is defined as sand with less than 3% moisture content. Preferably, the dry sand is between 1% and 0%. The frac-sand delivery may also use any other proppant such as man-made proppant that is less commonly used.

According to an embodiment depicted in FIG. 1, the frac-sand delivery system comprises a sand storage pit 10, a water pit or tanks 20, and a sand regulator 30 at the pad site. A more detailed view of the site layout is shown in FIG. 2. Wet or dry sand is transported directly from a wash plant to the sand storage pit 10 on site. See 220. The sand is then pumped as a concentrated slurry by a source pump 12 via pipe 14 to the sand regulator 30. Source pump 12 may be sitting in the regulator 30 or within the storage pit 10. Water 210, also defined as the clean stream, may be delivered from the water tanks 20 to the sand regulator 30 to be combined with the concentrated slurry, often referred to as the dirty stream, to make the appropriate PPA concentration. The flow, rate, and density of sand and water delivery to the frac pumps 50 is controlled by the sand regulator 30 directly or indirectly via a manifold 52 through supply lines 48. The clean stream and the metered concentrated slurry can be supplied to the manifold in a combined stream or kept separate as a split stream if desired so to only expose the subset of the frac pumps to the sand slurry and limit wear due to abrasion to fewer pumps. Chemical additives may be added to the sand slurry within the regulator 30. The combined stream or the two split streams along with the added chemicals are then injected to the wells 60 with the high pressure frac pumps.

The sand storage pit 10 may be a lined earthen pit, a temporary or permanent above the ground storage tank, slurry silos or any large capacity container. The sand, wet or dry, will be delivered and stored in the storage pit 10, eliminating the need for specialized storage. The sand storage pit 10 may be formed in an advantageous shape for funneling the sand downward toward the center of the pit, such as an inverted cone like shape as shown in FIGS. 3A and 3B or half inverted cone like shape such as shown in FIGS. 7A and 7B. Preferably, the lined pit may hold 1 to 3 million pounds of sand and 1 to 8 million gallons of water, but may be larger or smaller depending on job specs.

The sand storage pit 10 will reduce off load times at the pad site. Currently dry sand is transported by specialized pneumatic trailers or boxes. The pneumatic trailers use pressure to blow the load of dry sand into upright silos on site. The process takes as much as 45 minutes to off load dry sand. This is a substantial cost of transportation and effects the number of loads a truck can deliver in a 12-hour period. The storage box systems are more efficient to off load but require forklifts and other specialized conveyors. Additionally, the box and silo systems require annual leases that are very expensive to service companies. However, the sand storage pit 10 may enable side or belly dump trailers to dump directly into the pit at a truck of load site 230. This change in delivery trailer reduces off-load time, for example, taking less than 10 minutes. The time savings in off-loading will save on costs associated with pneumatic trailers. For example, reducing the off-load time by 30 minutes may provide savings of 20 to 30 percent of cost associated with pneumatic trailers. With regard to box storage systems, the frac-sand delivery system eliminates the forklift and custom trailer cost. Savings compared to box systems will be substantial, and may exceed 50 percent. The sand may also be transported via non-specialized hauling equipment such as dump trucks, temporary or permanent above ground pipeline runs, temporary or permanent below ground pipeline runs, or similar means.

The sand storage pit 10 may be centrally located to support multiple wells that may be placed on a section of land. For example, in the Delaware Basin, operators are placing as many as four 12-well pads on one section of land. Centrally locating the sand pit in the center of the section of the pad site would allow this single pit to support up to 50 well completions. This system will allow exploration and production operators in areas with multiple pay zones and multi-well pads to build water and sand pits that services as many as 10 to 100 well completions.

The sand regulator 30, an embodiment of which is shown in FIGS. 4A and 4B, regulates the amount of sand per gallon of water delivered to high pressure pumps or to the blender 40 by managing the flow and rate, and density of sand and water to the frac pumps 50. The sand regulator 30 may communicate electronically, through control logic, with the optional blender 40 to deliver sand as needed in the desired downhole rate and concentration of sand that is desired. The sand regulator 30 monitors the pounds of sand per gallon of water circulating from the storage pit 10. The sand regulator 30 may include a density meter 32, flow meter 34, flow rate sensor, and other sensors that monitor data, including but not limited to, Density Dredge Line (PPA), Flow Rate Dredge Line (BPM), Density to Blender (PPA), Flow Rate To Blender (BPM), Total Sand pumped per Stage (lbs), Total Sand Pumped (lbs), Water pumped per Stage (BBL), Total Water Pumped (BBL), Inputted Downhole Rate (BPM), Desired Downhole Density (PPA), Slurry per Stage Pumped (BBL), Total Slurry Pumped (BBL), and Sand Specific Gravity. The data collected by the sand regulator 30 is then sent to a control panel 42 and/or computer. The control panel may use control logic to calculate from this data the volumetric ratio per unit time (GPM, BPM, etc.) of clean water to dirty water required to be sent to the blender tub in order to dilute the slurry to the desired PPA value. Further, using a real time density reading, the control panel may determine how much flow is needed to provide the desired amount of sand to frac pumps, and open a supply valve 36 on a line delivering sand to the frac pumps and close return valves 38 on a return line to the sand pit 10 accordingly to achieve necessary rate to the tub. For example, the valves 36 and 38 may be pinch valves, butterfly valves and/or other suitable valves. The sand regulator 30 may be capable of delivering dirty water to the frac pumps 50 at a high rate of accuracy. For example, the sand regulator may allow to produce a range of 0.25 to 3 lbs of sand per gallon of water at a rate up to 100 BBL per minute. The components of the regulator can be sized to achieve higher pump rates and higher concentration if necessary.

The sand regulator 30 may be mobile, such as by mounting the regulator on a skid, or it may be installed as stationary equipment at the well site.

According to another embodiment depicted in the site layout in FIG. 5, a frac-sand delivery system comprises a sand storage pit 110, a source pump 120, and a sand slurry regulator 130. Water and sand slurry from the sand storage pit 110 are pumped by the source pump 120 to the sand slurry regulator 130, where density (PPA) and flow rate (BBM) are regulated to meet the requirements of the customer's frac design. The source pump 120 may be a submersible C-pump, a dredge pump, a centrifugal pump, an EDDY pump, a jet pump ejector/eductor), or similar pump, situated below the water surface at or near the pit bottom of the sand storage pit 110. For example, the pump may be situated 15 to 20 feet below water surface. In one embodiment, the sand slurry regulator 30 is used in a straight feed, as opposed to a closed loop, setting, and serves to meter and regulate the percent solids or PPA in the slurry of sand and water. In this embodiment, the sand slurry regulator 30 adjusts the density of sand and water delivery via flow rate adjustments, as opposed to looping back excess amounts of sand and water in a closed loop setting. Sand left in the storage tank may be pumped back to the source if necessary so to allow demobilization of the storage pit to the subsequent frac sites as needed.

The sand slurry regulator 130, an embodiment of which is depicted in FIG. 6A-6B, receives a homogenous sand slurry from the source pump and recirculate the slurry back to the sand storage pit 110. Water may be delivered from the water tanks 120 to the sand slurry regulator 130 and/or to the sand storage pit 110 to be added to the slurry, and the flow and rate of water may be adjusted by the sand slurry regulator 130 to achieve the desired PPA concentration. Chemical additives may also be added to the sand slurry within the sand slurry regulator 130. The PPA in the recirculating slurry may be measured, for example, by high frequency ultrasonic density meters 132. Once originating PPA is established, supply valve 136 and return valve 138 will open and close allowing the appropriate PPA to be delivered directly or indirectly to the frac pumps 150 via a supply line 148 (directly or indirectly, such as through a manifold 152) to be discharged to the well head 160, and the balance of the slurry will recirculate back to the storage pit via a return line 118. For example, the valves 136 and 138 may be pinch valves, butterfly valves and/or other suitable valves. Preferably, the delivered PPA ranges from 0.25 to 3 lbs/gal, and the rates range from 50 to 100 BPM. The flow and rate of the slurry may be measured by flow meters 134, and the valves 136, 138 can be adjusted to achieve a desired flow of flurry to be delivered to the frac pumps 150.

Current frac sand systems originate a sand slurry in an open top tub where sand is delivered in a dry or damp form using augers or conveyor systems and combined with water prior to being pumped to the missile. The blender tub agitates the slurry with paddles as sand is added into the tub. This process allows air bubbles to be captured in the slurry. When the air bubbles are exposed to the high-pressure pumps, microscopic explosions occur causing cavitation damage to pump fluid ends, which is a known industry issue. The sand delivery system addresses the air and cavitation issue by originating the sand slurry with the submersible pump 120, which is situated below the water surface level of the sand storage pit 110. Air will not be introduced at origination of the slurry due to the pumps submerged depth at origination, which will dramatically increase fluid end duty cycles. The sand delivery system therefore allows sand slurry to be introduced to high-pressure pumps while avoiding the negative impact of air bubbles.

While several embodiments have been provided in the present disclosure, it should be understood that the disclosed systems and methods may be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted or not implemented.

Additionally, other items shown or discussed as being in direct connection with each other may be indirectly connected or communicating through some interface, device, or intermediate component, whether mechanically, electronically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and could be made without departing from the spirit and scope disclosed herein. 

What is claimed is:
 1. A frac sand delivery system comprising: a pit for storing sand; a sand slurry regulator comprising: a supply line for receiving sand from the pit, a return line to return sand to the pit, a flow meter, and a density meter; and a source pump which pumps sand from the pit to the sand slurry regulator through the supply line, wherein the sand slurry regulator monitors at least one of the flow and density of the sand slurry and adjusts at least one of the flow and density to deliver slurry to a frac pump with a desired concentration of proppant added.
 2. The frac sand delivery system of claim 1, wherein the source pump is a submersible pump situated below the water surface of the pit.
 3. The frac sand delivery system of claim 1, further comprising a water line for supplying water to the sand slurry regulator.
 4. The frac sand delivery system of claim 1, further comprising a water line for supplying water to the pit.
 5. The frac sand delivery system of claim 1, wherein the pit is a lined earthen pit. 